Oxidative stress which results from an excessive accumulation of ROS has been implicated in a wide variety of human neurodegenerative disease. The superoxide dismutases (SODs), catalase (CAT) and glutathione peroxidases (GPxs) play key roles in the cellular defense against ROS. Each enzyme of this triad has a specific function and they act in concert in the inactivation of ROS. The brain tissue appears to be especially vulnerable to oxidative stress, since it contains almost no catalase activity and has comparatively low levels of glutathione, vitamin E and GPx. Familial amyotrophic lateral sclerosis (fALS) which is a progressive degenerative disorder of motor neurons, is associated with deficiencies in SOD1 activity. On the other hand, in Down's syndrome (DS) which resembles Alzheimer's Disease (AD) in its final phases, SOD1 is overexpressed due to trisomy of chromosome 21. It appears, therefore, that both underexpression and overexpression of antioxidant enzymes may result in brain pathology. In view of these observations, an investigation of the qualitative and quantitative interaction between these three enzymes becomes extremely important for understanding the causes and therapy of human neurodegenerative disorders. In the proposed project, we plan to examine the neuropathological consequences of imbalance in this triad of antioxidant enzyme by two complementary approaches: a) construction by homologous replacement of a variety of new transgenic neuronal and glial cell lines which can express SOD1, GPx-1 and catalase, individually or in combination, under the control of the Lac and/or Tet switches; b) use of a transgenic mouse model that we have already constructed which overexpresses human GPx-1 in several tissues including several brain regions. The transgenic cells, the transgenic animals and their appropriate tissues including several brain regions. The transgenic cells, the transgenic animals and their appropriate controls will be subjects to various treatment that are expected to produce oxidative stress in different ways in vivo and in vitro. Thus, the neuronal and glial cells will be exposed to a variety of pro-oxidant chemicals which are known to have different mechanisms of action and affect different properties of the cell. The transgenic and control mice will be exposed to ischemia/reperfusion which the hippocampal sections from these animals will be subjected to transient anoxic episodes. The effects of the above treatments will be assessed on a number of structural and functional parameters which are known to be critically influenced by oxidative stress, such as the integrity of DNA, protein, lipids, neuron-glia interaction as well as the expression of specific genes which are important in cell communications and signal transduction.